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Synthesis and Characterization of Microporous Titanium Silicates for Use as Proton Conducting Materials

Joseph J. Steirer Jr. and Yushan Yan. Chemical and Environmental Engineering, University of California, Riverside, 900 University Avenue, Riverside, CA 92521

High-silica-zeolite beta (BEA) and sulfonic acid functionalized beta (AF-BEA) have been synthesized and shown to have proton conductivity of 1.5 x 10-4 S/cm and 1.2 x 10-2 S/cm, respectively.1 AF-BEA-polymer composite membranes are shown to be effective for performance improvements of hydrogen and methanol fuel cells. In an effort of searching for better inorganic proton conductors, this study focuses on the synthesis and proton conductivity measurements of microporous titanium silicates. Due to the electron acceptor nature of the titanium atoms, microporous titanium silicates are potentially better proton conductors than silicates. The titanium silicates studied in this work are TS-1, AF-TS-1, Ti-BEA, ETS-4 and ETS-10. These materials are synthesized hydrothermally and characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM) with an energy-dispersive spectrometer (EDS), thermogravimetric analysis (TGA), infrared spectroscopy, Raman spectroscopy, powder x-ray diffraction (XRD), and proton conductivity measurements. The proton conductivity of TS-1 without and with tetrapropylammonium cation (TPA+) structure-directing agent is 1 x 10-4 S/cm and 3 x 10-4 S/cm, respectively, and AF-TS-1 with TPA+ structure-directing agent is 2 x 10-3 S/cm. The proton conductivity of ETS-10 ranges from 1-2 x 10-3 S/cm, which is ten times greater than the proton conductivity of BEA. This suggests that ETS-10 is a promising material for the preparation of composite fuel cell membranes.

1. Holmberg BA, Hwang SJ, Davis ME, Yan YS, MICROPOROUS AND MESOPOROUS MATERIALS 80 (1-3): 347-356 MAY 2 2005